Image processing apparatus and method for generating correction formula

1. An image processing apparatus comprising: a platen to support a sheet thereon; a light source that extends in a main-scanning direction and is configured to move in a sub-scanning direction and irradiate light onto the sheet as the light source moves in the sub-scanning direction; an image sensor configured to generate multiple line image data based on light reflected by the sheet and incident thereon, as the light source moves in the sub-scanning direction; and a processor configured to: i) generate a correction formula exclusively associated with a scanning position in the sub-scanning direction, based on a difference of brightness values between first line image data generated from scanning of the sheet at a reference position, and second line image data generated from scanning of the sheet at a comparative position that is apart from the reference position by predetermined scanning positions in the sub-scanning direction; and ii) carry out a correction process with respect to line image data generated when scanning the sheet at the scanning position to cause a brightness value thereof to be the same as the brightness value of the first line image data, using the correction formula.

2. The image processing apparatus according to claim 1 , wherein the comparative position is located forward relative to the reference position in the direction in which the light source moves during scanning.

3. The image processing apparatus according to claim 1 , further comprising: a data storage in which the correction formula is set.

4. The image processing apparatus according to claim 1 , wherein the processor is further configured to carry out a second correction process with respect to each pixel data in the line image data, using a second correction formula.

5. The image processing apparatus according to claim 4 , wherein the processor carries out the second correction process and then the correction process.

6. A method for generating and using a correction formula for line image data obtained by an image processing apparatus during scanning of a sheet at a scanning position in a sub-scanning direction, the method comprising: moving a light source that extends in a scanning direction, in the sub-scanning direction, through a reference position and then a comparative position that is apart from the reference position by predetermined scanning lines, while the sheet is placed on a scanning window of the image processing apparatus; generating first line image data at the reference position and second line image data at the comparative position; generating a correction formula exclusively associated with the scanning position, based on a difference of brightness values between the first and second line image data; and carrying out a correction process with respect to line image data generated when scanning the sheet at the scanning position to cause a brightness value thereof to be the same as the brightness value of the first line image data, using the generated correction formula.

7. The method according to claim 6 , wherein the comparative position is located forward relative to the reference position in the direction in which the light source moves during scanning.

8. The method according to claim 6 , further comprising: storing the generated correction formula in a data storage.

9. The method according to claim 6 , further comprising: carrying out the correction process with respect to line image data generated through subsequent scanning of a sheet at the scanning position by the image processing apparatus, using the generated correction formula.

10. The method according to claim 9 , further comprising: carrying out a second correction process with respect to each pixel data in the light image data, using a second correction formula.

11. A non-transitory computer readable medium comprising a program that is executable in a computing device to cause the computing device to perform a method for generating and using a correction formula for line image data obtained by an image processing apparatus, the method comprising: controlling a light source that extends in a scanning direction, to move in a sub-scanning direction, through a reference position and then a comparative position that is apart from the reference position by predetermined scanning lines, when determining that the sheet is placed on a scanning window of the image processing apparatus; receiving first line image data generated when the light source is at the reference position and second line image data generated when the light source is at the comparative position; generating a correction formula exclusively associated with a scanning position, based on a difference of brightness values between the first and second line image data; and carrying out a correction process with respect to line image data generated when scanning the sheet at the scanning position to cause a brightness value thereof to be the same as the brightness value of the first line image data, using the generated correction formula.

12. The non-transitory computer readable medium according to claim 11 , wherein the comparative position is located forward relative to the reference position in the direction in which the light source moves during scanning.

13. The non-transitory computer readable medium according to claim 11 , wherein the method further comprises: storing the generated correction formula in a data storage.

14. The non-transitory computer readable medium according to claim 11 , wherein the method further comprises: carrying out the correction process with respect to line image data generated through subsequent scanning of a sheet at the scanning position by the image processing apparatus, using the generated correction formula.